Process of manufacturing paper and paper board



Patented Aug. 11, 1936 PROCESS OF MANUFACTURING PAPER AND PAPER BOARD Levis Miller Booth, Plainfield, N. J.

No Drawing. Application July 20, 1932,

Serial No. 623,602

12 Claims.

This invention relates to the manufacture of paperproducts by the aid of acidulated water.

In the manufacture of some grades of paper and board the vehicle water becomes acldulated, because (a) the stock is of an acid nature, (1)) it becomes acidulated by bacterial action incidental to decomposition of the fibre stock (0) by the action of acidifying substances added to the fibre stock during the process of manufacture, or the acidity may be imparted by impurities which are present in the fresh water which is used for Vehicle water. I

In the prior art the means provided to control the extent of acidity have been inefficient thereby resulting in variations in the quality of the finished product and furthermore the speed of production has been less than that which is possible when my improved process is employed.

The principal object of this invention is to control the extent of acidity of the vehicle water at a late stage in the paper making process. The means for so doing are novel, effective, and cheap.

The term paper, as used herein includes not only what is commonly known as paper, but also paper boards of various kinds, and includes products composed primarily of fibrous substances which are conveyed and processed as liquid suspensions.

In the manufacturer of paper, sulphate of aluminum, commonly known as paper makers alum is usually employed for the precipitation of resin size, for setting coloring matter, to cause a desired astringency of the stock or to convert the bicarbonate hardness of the water intosulphate hardness. The paper maker predicates the amount of alum to be added to the furnish upon experience based on judgment of the quality of previous lots of finished paper, or he depends on chemical test procedure. The customary practice in the latter instance'is to add enough of alum to produce the extent of acidity desired, as determined by pH or titration measurements. The control tests are commonly made on samples taken at the beater.

In the formation of paper the essential elements are, (a) the fibre and other paper making solids, and (b) the vehicle water. One or both of these essential elements is responsible for the presence of carbon dioxide, either free or loosely held in combination. This carbon dioxide tends to escape from the vehicle water at, or just prior to, sheet formation, at the time'when the liquid is subjected to the minimum pressure. The release of gas at this stage of the process causes interference with the desired tendency of the fibres to become felted in good formation on the paper making wire, and thereby results in a sheet of diminished strength when formed in the presence of escaping gas; also the finish of the sheet is adversely influenced.

' In measuring the quantity of acidity of the paper making vehicle water, I- employ the prescribed procedure for determining total acidity as published in Standard Methods of Water Analysis, sixth edition, 1925, by the American Public Health Association andAmerican Water Works Association. 1

Tests should-be made to measure both the intensity andquantity of acidity to serve as a guide Where accurate control is desired. These tests are expressed in terms of pH and total acidity. If this practice is followed, the confusion which results from reliance on one or other of these tests is obviated. Among many paper makers the general impression prevails that theacidity oxide prevailing at the time the sheet is formed.

pH tests of the vehicle water made on samples taken following the application of my prescribed chemical treatment, whichreduces the free carbon dioxide content to the desired minimum are therefore not so apt to be misleading as is the case when my compensating treatment is not applied.

In making paper by my improved process I follow the customary .procedure of adding size,

alum, etc, during the early stage of the process.

Later, preferably just before water carrying the stock goes to the paper forming wire, I add a counteracting chemical which has the effect to 'reduce the total acidity to the desired point by eifecting chemical combination of the acidifying substances present in the vehicle water. At this stage of the paper making operation the consistency is usually less than two (2%) percent. I may use sodium phosphate compounds, borax or sodium silicate. I have successfully used calcium, magnesium and sodium hydroxides as well as sodium aluminate. Other oxides or hydroxides having affinity for carbon dioxide may be used to g In this process it is not desirable to apply sulficient compensating reagent to cause the vehicle water or the stock to become alkaline. I prefer to retain always enough of acidity to show positive values as measured by the method referred to for determining total acidity. Naturally, since carbon dioxide is detrimental in the formation of a sheet, I do not use any alkali which when decomposed will yield carbon dioxide. I employ only 'alkalies which combine with or which will reduce the amount of free carbon dioxide present in the vehicle water. This phase of water treatment differs from that involved in: water softening wherein chemical combination with carbon dioxide is effected. In the latter instance insoluble carbonate compounds are formed. In the present process I add a control reagent to react with the carbon dioxide to form bicarbonates which are water soluble compounds. In some cases I form soluble carbonates. I do not add control reagent in sufficient amount to form insoluble carbonate substances, at least at the temperature and under the conditions prevailing at the point of application. v

By the addition of hydrated lime to a water containing carbon dioxide bicarbonate of lime is formed. This latter is then available to effect precipitation of aluminum hydroxide as a result of combination with aluminum sulphate which may be present in the water.

The use of alkalies such as I employ successfully, when applied in quantities sufiicient to reduce the total acidity of the vehicle water below the desired minimum, is detrimental to resin sizing and to certain coloring materials used in paper making. Since this fact is universally recognized by paper makers, the use of such alkalies as I employ for this purpose has been deemed to be outside the bounds of reason. However, by the judicious application of these otherwise detrimental substances, I am'able to produce paper of improved formation, strength and finish and also to obtain better bending and fold ing qualities without diminishing the other desirable characteristics of the sheet.

The following example is cited. A sample of vehicle water taken before the application of my compensating treatment may test as follows:

pH 4.5; total acidity 37.0 parts per million.

After my treatment the same would test approximately:

pH 4.5; total acidity 27.0 parts per million. Since the difference-10.0 partsrepresents acidifying substances which are detrimental in paper making, it is apparent that the compensating treatment is beneficial.

There are some kinds of paper which may be improved by the use of compensating reagents of these feeders may be equipped with automatic pH controllers if desired.-

By the use of my process, involving chemical treatment close to the point of sheet formation, the quality of the vehicle water may be controlled to a degree of uniformity not possible by the application of chemicals during the earlier stage of processing. Moreover improved quality of the product is insured.

I claim:

1. The method of making paper which consists of adding an alkaline substance which has a water solubility in excess of fifty (50) parts per million at such rate as to react with a portion of the water soluble substances in the vehicle Water to the stock after the stock has been diluted to a consistency of less than two (2) parts of stock to ninety-eight (98) parts of water and subsequently forming paper.

2. The method of making paper which consists of adding an alkaline substance which has a water solubility in excess of fifty (50) parts per million at such rate as to react with a portion of the Water soluble substances in the vehicle water to the stock after the stock has been diluted and at a time not in excess of five minutes before the subsequent formation of paper.

content of the diluted stock to the stock having a consistency of less than 2% at a time not in excess of five minutes before forming the sheet and subsequently forming paper.

5. The method of making paper which con sists of adding an amount of caustic soda less than that chemically equivalent to the acidic content of the diluted stock to the stock at a time when the stock has a consistency of less than 2% and subsequently forming the paper.

6. The method of making paper which consists of adding an amount of caustic soda less than that chemically equivalent to the acidic content of the diluted stock to. the stock having a consistency of less than 2% at a time not in excess of five minutes before forming the sheet and subsequently forming the paper.

7. The method of making paper which consists of adding to the stock having a consistency of less than 2% an amount of reagent less than that chemically equivalent to combine with the acidic content of the diluted stock which will combine with the acid salts present without causing evolution of carbon dioxide and subsequently forming paper.

8. Themethod of making paper which consists of adding to the stock having a consistency of less than 2% an amount of reagent less than that chemically equivalent to the acidic content of the diluted stock which will combine with the acid salts present without causing the evolution of carbon dioxide at a time not in excess of five minutes before forming the sheet and subsequently forming paper.

9. The method of making paper which consists of adding an amount of hydrated lime less than that chemically equivalent to the acidic content of the diluted stock to the stock at a time not in excess of five minutes before the subsequent formation of the paper.

10. The method of making paper which consists of adding an amount of sodium silicate less than that chemically equivalent to the acidic content of the diluted stock to the stock at a time not in excess of five minutes before the subsequent formation of the paper.

,sists of adding an amount of alkaline hydroxide substance less than that chemically equivalent to the acidic content of the diluted stock to the stock after the stock has been diluted to a. consistency of less than a ratio of two (2) parts of stock to ninety-eight (98) parts of water and subsequently 5 forming paper.

LEVIS MILLER BOOTH. 

